The dark spot on the toe is evidence that the finish and perhaps even the leather (is it shell? if not then the grain surface of the leather) itself has been damaged. The leather in that area is absorbing wax, oils, dyes,etc., at a different / greater rate than the more impermeable leather surrounding it. It is like a very, very, superficial scuff.
If that analysis proves correct, there's not much that can be done to bring it back. Sorry. I hope I'm wrong.
This seems to be the issue. The first thing that needs to be done is the oil, or grease, or whatever is sitting in there needs to be wicked up using a solvent like Renomat or turpentine or something and allowed to dry. After that if the area is still dark applying some white vinegar on a small piece of paper towel and sticking it to the toe over the spot and pulling some cling wrap over it to slightly control evaporation and leaving it over night can help. After removing it let it sit a little while longer.